What are algal blooms? And what do they have to do with climate change?

Following on from my previous post last week, I will today be discussing the implications of eutrophication.

Algal blooms are formed from microalgae (or phytoplankton) they are single celled plants, which live in the ocean. Phytoplankton are buoyant and so they live in the upper part of the water column called the photic zone, it is the depth of light penetration in the water. This is important as these organisms live by photosynthesis.

Macro algae grow so quickly and cover so much surface area that the algal blooms prevent sunlight from reaching other plants stopping photosynthesis and resulting in a lack of oxygen in the water. They also impact other organisms by releasing natural toxins which are harmful to animals, humans and even livestock.

Cyanobacteria (blue-green algae) are also photosynthetic bacteria which occur naturally in both freshwater and marine water bodies. Blue- green algae are known to be the most commonly toxic bloom, other blooms can also be caused by dinoflagellates in marine or estuarine water bodies these are the red tides that we see. However, not all harmful algal blooms are visible by the human eye.

Algal blooms occur as a result of these microalgae overgrowing and creating dense clouds in the water. Algal blooms are a natural occurrence but eutrophication is causing them to be far more common and harmful. An influx of nitrogen and phosphorous into water causes overgrowth of algae. Combinations of environmental factors are required for algal blooms to form: Warm waters, plenty of sunlight, large amount of nutrients and high CO2 levels. Which are incidentally are all affects of climate change.

“Scientists predict that climate change will have many effects on freshwater and marine environments. These effects, along with nutrient pollution, might cause harmful algal blooms to occur more often, in more waterbodies and to be more intense.”

But it’s not all doom and gloom, scientists working at the National Oceanographic and Atmospheric Administration (NOAA) have been collaborating with universities in the Gulf of Maine to the Puget Sound to develop new systems that are able to track and predict harmful algal blooms (HAB). In Massachusetts, scientists have been experimenting with a sensor that is able to identify three different types of dangerous microscopic algae, which then offers an early warning if they’re detected in the water. In the Gulf of Mexico, NOAA’s HAB Forecasting System pulls together satellite imagery, information about water conditions gathered by weather buoys, and observations from scientists in the field to map blooms and predict how they will spread.

Knowing when and where HABs are likely to occur can help scientists and public officials minimize harm to people and marine life. And learning more about the causes of the blooms may ultimately help us prevent them.

To read more and learn about the climate impacts on harmful algal blooms visit: